454 XXXII. CELL-DIVISION AND NUCLEAR DIVISION. 



only after the sections fixed on the object-slide have first been 

 soaked in 1 per cent, chromic acid. The object-slide with the 

 sections is for this purpose left for twenty-four hours in the 

 chromic acid, then transferred to pure water and there left to 

 wash for two hours. Under no circumstances, however, will the 

 staining proceed unless all the paraffin has been removed from the 

 section by washing in turpentine and afterwards in absolute alcohol. 



The objects must be laid for a day, in some cases longer, 1 in a 

 dark alcoholic solution of safranin. For this purpose one uses a 

 concentrated solution of safranin in alcohol, to which an equal 

 volume of water and a little aniline water have been added. The 

 sections are then treated with alcohol, 2 and then with alcohol to 

 which Ol per cent, hydrochloric acid is added, and then again 

 washed with pure alcohol. This washing must be done very care- 

 fully in order that too much safranin should not be removed from 

 the sections. In general the needful degree of decolorising is very 

 quickly attained. The object-slide is then placed for about ten 

 minutes, under some circumstances, however, much longer, in a 

 dark (concentrated) watery solution of gentian-violet. It is then 

 rapidly washed in water, or sometimes without this, and placed 

 in a dark (concentrated) watery solution of orange G. 3 which is 

 allowed to set for about two minutes. In this fluid the dark 

 colour is gradually dissolved out, and, while blue clouds of colour 

 are still rising, the sections are washed in neutral absolute alcohol, 

 renewed several times ; then transferred to oil of cloves for so long 

 as blue clouds of gentian colour come out of the section, when it is 

 finally mounted in Canada balsam dissolved in xylol, and covered 

 with a cover-glass. Care must be taken that not more Canada 

 balsam is placed under the cover-glass than will occupy the given 

 space. That only thin cover-glasses must be used goes without 

 saying, bearing in mind the high powers we shall wish to examine 

 the preparation with ; and it is well to obtain extra large cover- 

 glasses whereby proportionately longer series of sections may be 

 covered. 



The critical matter in this method of staining is to determine 

 the exact point at which staining or decolorising should be stopped. 

 Hence the length of action of the separate stains, and of their sub- 



1 Plemming recommends two or three days. [Eo.] 



2 Zimmerman, Botanische Microtcchnik, recommends water. [Eo.] 

 :! One of Grubler's stains; obtainable from Southall Bros. & Barclay, 



Birmingham. 



